(1) Field of the Invention
The present invention relates to a sealing compound excellent in the adaptability to the lining operation. More particularly, the present invention relates to an improvement in a sealing compound comprising as the main ingredient an aqueous latex of a styrene-butadiene rubber.
(2) Description of the Prior Art
In the conventional process for the manufacture of cans, a liquid sealing composition called "sealing compound" is lined in an annular groove of a can end member (can lid), and a sealing compound layer (gasket) is thus formed, if necessary, by drying. Then, the can end member is double-seamed to a flange of a can body to form a can.
This sealing compound comprises as the main ingredient an aqueous latex of a styrene-butadiene rubber (SBR) which contains styrene-butadiene rubber particles ordinarily having a number average particle size of from 1200 to 1500 A. When this known sealing compound is lined on a can lid at a relatively low speed, for example, of 20 to 150 strokes per minute, satisfactory results are generally obtained. However, it has been found that when the lining operation is carried out at a relatively high speed, for example, of 180 to 400 strokes per minute, problems arise in connection with the adaptability of this known sealing compound to the lining operation and the sealing performance and other qualities of the formed gasket.
More specifically, the above-mentioned latex-based sealing compound is lined in a groove formed on a can lid through an openable and closable nozzle, and the sealing compound undergoes a mechanical friction by sliding or the like repeatedly between a needle for opening and closing this nozzle and a leakage-preventing packing arranged along this needle. This mechanical friction is increased as the lining stroke number per minute is increased, and with increase of this mechanical friction, the temperature of the sealing compound is elevated.
In the above-mentioned conventional sealing compound, at the time of the high speed lining operation, agglomerates of the rubber particles are formed and coagulated by the mechanical friction and/or the elevation of the temperature, and simultaneously, the viscosity of the sealing compound is increased. As the result of that long-time continuous lining operation becomes impossible and the adaptability to the lining operation is degraded. Furthermore, the sealing performance of the formed gasket becomes insufficient and other qualities and properties of the gasket are degraded.